For a number of years continuous casting of metals such as aluminum, lead, zinc, and the like has been conducted in commercial scale operations with continuous casters such as shown in U.S. Pat. Nos. 2,790,216 or 4,054,173, both of which are incorporated herein by this reference. Such a continuous caster comprises a pair of rotating water-cooled rolls. Molten metal, for example aluminum, is fed into the nip of the rolls just prior to the line of closest approach of the two rolls. Heat is rapidly extracted from the molten metal by contact with the rolls, and freezing occurs before the metal reaches the line of closest approach to the rolls.
With such a caster, metal sheets a couple of meters wide and about one centimeter thick can be continuously cast at rates of more than a meter per minute for several days at a time. One important aspect of such a continuous caster is the tip which is used to feed molten metal into the nip of the rolls.
Molten metal feed tips comprise a pair of spaced-apart plates between which the molten metal flows. At the downstream end of the tip, the outer surface of the plates converge, reducing the thickness of the tip at its downstream end, enabling the tip to fit closely into the nip of the rolls.
The plates of the tips are made out of multiple segments, rather than a single integral piece of material. This is done for several reasons. First, the use of multiple segments enables the width of the tip to be varied by simply varying the number of segments in each plate. This enables a single small mold to be used to make tips of various sizes rather than requiring a separate large mold for each desired tip size. Since molds are very expensive to build, this makes multiple segment plates much more economical than plates made of a single integral piece of material. In addition, wide, non-segmented or single piece plates tend to warp, particularly at their downstream edges, and hence, cannot be used.
The molten metal feed tips are made of heat resistant insulating materials which are non-wettable by the molten metal. Exemplary of such materials is an asbestos fiber-containing composition sold by Johns Manville Co. under their trademark Marinite and refractory fiber-containing compositions sold by the Carborundum Co. of Niagara Falls, N.Y., under their trademarks Fiberfrax and Kaowool.
These materials are not very strong. As a result, the tips tend to break or chip, particularly at their thin downstream edges and must be replaced. Once a broken tip has been removed from the tip holder of the casting machine, the various pieces of the new tip are assembled onto the holder. Once the pieces have been fully assembled, the outside faces of the various segments of the plates must then be sanded at their downstream ends to form a smooth flat surface which will fit uniformly into the nip of the rolls. The assembly of the tip and the sanding take a great deal of time during which the caster cannot be used. Accordingly, tip replacement tends to be a very costly procedure.